1. Field
The present disclosure relates generally to ultrasonic inspection and in particular to a method and apparatus for identifying undesirable conditions in an object using ultrasonic inspection. Still more particularly, the present disclosure relates to a method and apparatus for positioning ultrasonic transducers generally adjacent to the surface of an object.
2. Background
Aircraft are being designed and manufactured with greater percentages of composite materials. Some aircraft may have more than fifty percent of their primary structure made from composite materials. Composite materials are being used in aircraft to decrease the weight of the aircraft. This decreased weight improves payload capacities and fuel efficiencies. Further, composite materials also may provide improved corrosion and fatigue resistance for various components in an aircraft.
Composite materials are tough, light-weight materials created by combining two or more dissimilar components to create a component with stronger properties than the original materials. Composite materials are typically non-metal materials. For example, a composite may include fibers and resins. The fibers and resins may be combined by curing or heating these components to form a cured product for the composite material.
In particular, key components, such as wings and fuselage skins, are now being constructed exclusively with composite materials, such as a composite laminate. With more and more critical structures being made of composite laminates, methods and techniques to assure that these components meet quality standards are needed more than ever before.
Porosity is an example of known undesirable condition that may occur during processing to create composite components. Porosity occurs when voids are present in a material caused by evolved gases. Currently, much time, effort, and money is spent on ultrasonic measurement systems that are designed to detect and quantify the porosity in composite components, such as those made using carbon laminates. Other examples of undesirable conditions include, for example, the presence of foreign materials or debris within the component and delamination.
Ultrasonic testing involves sending ultrasonic pulse waves into an object to detect undesirable conditions or to characterize materials. In ultrasonic testing, one or more ultrasound transducers are passed over an object that is being inspected. The transducers are typically separated from the test object by a coupling material. This coupling material may be, for example, a liquid such as oil or water. The same ultrasound transducer may send and receive ultrasound signals. In other advantageous embodiments, one ultrasound transducer may be used to transmit the ultrasound through the surface while a separate receiver detects the ultrasound that has reached the other surface after travelling through a medium. The coupling material is used to prevent signal loss. In this manner, undesirable conditions may be detected.
Typically, the ultrasound transducer or transducers are placed into a housing that positions the ultrasound transducer over the object. The design of the housing may be such to allow a maximum area of inspection. Maintaining the coupling between the transducer and the surface of the object may be challenging in some situations. For example, if the object being tested is too large to immerse within the coupling material, the housing may supply the coupling material in the manner to maintain the coupling material between the transducer and the surface of the object.
Retaining or maintaining sufficient coupling material may be performed through the design of the housing. Many designs are suitable for use on flat surfaces. However, when the same housing is used on a curved surface, is often difficult to maintain sufficient coupling thread to perform an inspection. This type of situation may occur with the fuselage of an aircraft. If the housing containing the transducer is moved longitudely, the surface maintains a constant curve. If the housing is turned to move around the longitudinal axis, then the shape of the housing may no longer fit the curvature of the surface. In this case, a different housing may be needed.
One solution currently used for this problem is to employ a bladder. The bladder encapsulates or contains the coupling material and is placed between the housing and the surface of the object. One drawback of the bladder is increased friction on the surface on the part. This type of friction may cause the housing to move in a manner that causes a loss in the ultrasonic signal.
Further, the use of a bladder requires more area around a transducer to incorporate the bladder into the housing design. The increased area around the transducer also may result in loss inspection area near the edges of the part to be inspected. Further, with a bladder it is important that all of the air is removed from the bladder before the inspection begins. Therefore, it would be advantageous to have an improved method and apparatus for performing ultrasonic inspections of objects.